Field of the Invention
The present invention relates to an operation control apparatus for an internal combustion engine in which a variable valve operating system is assembled.
Description of the Related Art
Variable valve operating systems are known which enable a change in the valve timing or lift of an intake valve and/or an exhaust valve in order to optimize, for example, an output property of an internal combustion engine according to an operation state of a vehicle. Some of these variable valve operating systems are well known from Japanese Patent Laid-Open No. 2008-151037, Japanese Patent Laid-Open No. 2009-264200, and the like; in the variable valve operating systems disclosed in these patents, for a single valve, a plurality of cams with different cam profiles and a plurality of rocker arms with which the respective cams are contact with are selectively allowed to function. Advantageously, the variable valve operating systems that allow the plurality of rocker arms to selectively function for the individual valves can be configured at relatively low cost compared to variable valve operating systems based on other schemes.
In such a variable valve operating system, the valve timing and the lift of the intake valve/exhaust valve are changed according to the quantity of fuel supplied to the internal combustion engine mounted in the engine, that is, a fuel injection quantity, and the rotational speed of a crank shaft in the internal combustion engine, that is, an engine speed. In general, the rocker arms to be used are selected such that the intake valve/exhaust valve has a high lift in an operation region with a high engine speed and a large fuel injection quantity, whereas the intake valve/exhaust valve has a low lift in an operation region with a low engine speed and a small fuel injection quantity.
In the variable valve operating systems disclosed in Japanese Patent Laid-Open No. 2008-151037 and Japanese Patent Laid-Open No. 2009-264200 and allowing the plurality of rocker arms to selectively function for the individual valves, spring forces are applied by lost motion springs to the respective rocker arms other than those which are constantly contact with the intake valve/exhaust valve via auto lash adjusters.
In recent years, attempts have been being made to reduce the internal resistance of the internal combustion engine itself in order to increase fuel efficiency. In this regard, the spring forces of the lost motion springs assembled in the variable valve operating system described in Japanese Patent Laid-Open No. 2008-151037 and Japanese Patent Laid-Open No. 2009-264200 may be a factor that increases the internal resistance of the internal combustion engine itself. In particular, a very large value is set for the spring forces of the lost motion springs applied to the rocker arms to temporarily open the exhaust valve in the initial stage of an intake stroke of the internal combustion engine to add a portion of hot exhaust gas to cool intake gas in order to improve ignitability of fuel in a cold state. Thus, the internal resistance of the internal combustion engine is comparatively increased or reduced depending on whether or not the spring forces of the lost motion springs are applied to the intake valve/exhaust valve according to the operation state of the vehicle. For example, when a secondary battery mounted in the vehicle is to be efficiently charged, the internal resistance of the internal combustion engine may be effectively reduced by selecting cams and rocker arms that allow for a reduction in the lift of the intake valve/exhaust valve. When an engine brake is to be more effectively applied during deceleration of the vehicle, the internal resistance of the internal combustion engine may be effectively increased by selecting cams and rocker arms that temporarily open the exhaust valve in the initial stage of the intake stroke of the internal combustion engine.
However, the conventional variable valve operating systems select a combination of cams and rocker arms to be allowed to function only based on the engine speed and the fuel injection quantity. Thus, the conventional variable valve operating systems fail to select a combination of cams and rocker arms allowed to function in accordance with a request for an increase or a reduction in the internal resistance of the internal combustion engine.